What happened
On the evening of February 21, 2003, a Mudry Cap 10 B, registration F-BUDJ, was conducting aerobatic training maneuvers near Pau, France. The flight, involving an instructor and a student pilot, began with the aircraft fueled with 72 liters of fuel. After departing from runway 31 and climbing to 3,500 feet, the crew began a series of aerobatic figures.
During a half-loop maneuver, while the aircraft was experiencing approximately 2G of acceleration, the instructor observed debris passing in front of the windshield. Upon leveling the aircraft, the instructor noticed the forward fuel tank cap was missing, while the student pilot reported an object obstructing the foot pedals. Upon checking the flight controls, the instructor discovered that the left rudder pedal was jammed in the neutral position and the fuel selector valve could no longer be operated. Recognizing that the fuel tank had become dislodged, the instructor initiated an emergency landing. Due to the wind conditions and the restricted rudder movement, the crew opted to land on runway 13, completing the landing without further incident.
The investigation
The investigation focused on the mechanical failure of the fuel tank mounting system. Examination of the aircraft revealed that the plywood surrounding the fuel tank cap had been damaged and the metal strap securing the forward tank had snapped at a mounting hole.
Metallurgical analysis of the broken strap determined that the failure was caused by fatigue. Investigators found that this specific strap had remained in service since the aircraft's manufacture. The investigation also noted that while routine maintenance inspections included a visual check of these straps, the inspection process was difficult and insufficient for detecting early signs of fatigue or aging.